C / C++ / MFC

m_hIOCompletionPort = CreateIoCompletionPort(INVALID_HANDLE_VALUE, NULL, 0, 0);

SOCKET socket = WSASocket(pAddrInfo->ai_family, pAddrInfo->ai_socktype, 0, NULL, 0, WSA_FLAG_OVERLAPPED);

if (bind(socket, pAddrInfo->ai_addr, pAddrInfo->ai_addrlen) == SOCKET_ERROR)
{
...
}

CreateIoCompletionPort((HANDLE)socket, m_hIOCompletionPort, (DWORD)pClientContext, 0);

// I have 8 worker threads in this case, post initial recv

for (int nIndex = 0; nIndex < m_nThreadCount; nIndex++)
{
	SOCKADDR_STORAGE addr;

	addr.ss_family = AF_UNSPEC;
	addr.__ss_align = 0;

	int nAddrLen = sizeof(SOCKADDR_STORAGE);

	DWORD dwBytesSent = 0;
	DWORD dwFlags = 0;

	char szBuffer[MAX_BUFFER_SIZE];
	ZeroMemory(szBuffer, sizeof(szBuffer));

	WSABUF wsaBuf;

	wsaBuf.buf = szBuffer;
	wsaBuf.len = sizeof(szBuffer);

	OVERLAPPED overlapped;
	ZeroMemory(&overlapped, sizeof(OVERLAPPED));

	int nResult = ::WSARecvFrom(socket, &wsaBuf, 1, &dwBytesSent, &dwFlags, (sockaddr*)&addr,
							&nAddrLen, &overlapped, NULL);

	int nError = WSAGetLastError();

        // nResult = 1, nError = IO_PENDING which is ok since no data has arrived yet 
}

// create the 8 worker threads now

	while (WaitForSingleObject(m_hShutdownEvent, 0) != WAIT_OBJECT_0)
	{
		CClientContext* pClientContext = NULL;
		OVERLAPPED* pOverlapped = NULL;
		DWORD dwBytesTransferred = 0;
		DWORD dwFlags = 0;
		WSABUF* pWSABUF = NULL;

		BOOL bReturn = GetQueuedCompletionStatus(m_hIOCompletionPort, &dwBytesTransferred,
												 (LPDWORD)&pClientContext, &pOverlapped, INFINITE);

  // if it got here, I'm assuming the data is in the buffer and ready to go, no?

						SOCKADDR_STORAGE from;
						int nFromLen = sizeof(SOCKADDR_STORAGE);
						memset(&from, 0, sizeof(SOCKADDR_STORAGE));

						int nBytesRecv = -1;

							nBytesRecv = WSARecvFrom(pClientContext->GetSocket(), pWSABUF, 1, &dwBytesTransferred,
													&dwFlags, (sockaddr*)&from, &nFromLen, pOverlapped, NULL);
						


						int j = WSAGetLastError();
						int k = 0;


// PROBLEM is here!! nBytesRecv is still -1 and WSAGetLastError() is still 997 :(. It is my understanding that GetQueuedCompletionStatus() will block until buffer is ready? That is how it works on TCP at least.
						}

}

int nBytesRecv = -1;
nBytesRecv = WSARecvFrom(pClientContext->GetSocket(), pWSABUF, 1, &dwBytesTransferred, &dwFlags, (sockaddr*)&from, &nFromLen, pOverlapped, NULL);
int j = WSAGetLastError();

Jochen Arndt wrote:

I have never used GetQueuedCompletionStatus(), because blocking
functions may cause problems. E.g. your shut down event will be only processed
after the blocking function returns. If the network connection of the system
drops, this will never occur.

Jochen Arndt wrote:

To test your code, you should check the return value of
GetQueuedCompletionStatus(), and test if bytes has been read
(dwBytesTransferred).

Jochen Arndt wrote:

You should also test your code with only one thread first to ensure that
problems are not sourced by using multiple threads. In your code you are
starting 8 receives in a loop where each uses the same variables. I'm not sure
if that is working.

Jochen Arndt wrote:

WSARecvFrom() does not return the number of bytes reads. It returns
0 upon success. Upon success you should not call GetLastError()
because it returns the most recent error which may be from any previous called
function that fails. Alternatively, you can call SetLastError(0)
before executing a function that may set an error value.

SledgeHammer01 wrote:

So I need to derive a new struct from OVERLAPPED and add the shared members there for UDP and pass that around.

KASR1 wrote:

How to resolve this error?